U.S. Pat. No. 3,945,770, of this inventor, discloses a high pressure pump. That pump describes a solid, nonyielding reciprocating member. It reciprocates towards an opposing resilient plug. The plug is supported by a nonyielding member also. The resilient plug incorporates a dished area which collapses on pressing the components together and the squeeze created by this collapse forces gas or liquid, captured in the dished area, through a passage. This disclosure sets forth an improved passage construction. The reciprocating member must terminate in a solid face, and the solid face is ordinarily constructed by fabricating a threaded cap. The threaded cap has a specific wall thickness, and a thin passage is drilled through this wall to center at the dished area. This is the outlet path. This passage has a finite volume which is a dead volume. That is, the dished area can be collapsed on application of pressure until there is no remaining volume in the dished area. The sample which is forced from the dished area must be forced through the narrow passage. This is a dead volume, namely the volume of the passage. The passage ordinarily terminates at a check valve to prevent back flow. The check valve is ordinarily arranged at the end of the passage, but it nevertheless cannot prevent the passage from collecting a dead volume which is not evacuated on each stroke of the sample collection apparatus.
An alternate form of sample collection apparatus uses a movable piston which reciprocates in a cylinder to admit the sample; the piston is forced along the cylinder to pressurize the sample to flow into a passage and through a check valve.
By contrast, this apparatus sets forth an improved passage construction. It is particularly improved in that the volume of the passage is substantially reduced. This construction substantially eliminates the dead volume in the passage. It is accomplished by positioning a check valve element in the altered passage which extends to the face of the anvil. That is to say, there is no passage volume left when the check valve is in position. The check valve can be forced open so that the passage permits flow in the intended manner; when it is closed, it closes fully and substantially fills the passage so that the check valve element is flush with the face of the anvil for all practical purposes.
The reduction of the fluid passage dead volume to a zero value enables collection of all of the sample which is captured by the device. It, thereby, enables the device to collect the sample volume more accurately. As the sample is collected, it must be forced pass a check valve. Some type of check valve arrangement is required to prevent the sample from trickling back out of the sample collection apparatus. One kind of check valve is a spring forcing a ball valve element against a seat, and this has worked quite well. An alternate form of check valve element utilizes an elongate pin with large shoulder to seat against the back face of the anvil wherein the pin protrudes into the passage to guide and align the check valve element. This again uses a return spring.
The return spring is a relatively small spring located in a relatively small chamber. Such a small spring can only, of necessity, provide a relatively small thrust. The force applied by the spring against the valve element, when considered in the abstract, should be sufficient to simply hold the valve closed. However, pressure variations in the sample collection system and the pipeline pose problems for the spring. Assume that the spring asserts a force sufficient to hold the check valve closed against the normal operating pressure in the pipeline and assume that is a value of 500 psi. Assume that the pipeline is designed for a maximum pressure of 800 psi. While the pressure will normally be maintained around 500 psi by the ordinary operation of the pipeline, inevitably, pressure surges will occur in the pipeline. Assume that a pressure surge transit occurs which increases the pressure to 750 psi for five seconds. In that event, the check valve spring will be overcome and sample will be forced continuously pass the check valve into the sample collection apparatus. This can be overcome by utilizing a spring of sufficient strength to overcome 800 psi, the rating of the pipeline. However, such springs must inevitably be larger to provide the increased spring force. There is a constraint on space, and it is not easy to provide such a strong spring for incorporation in such a small space.
The spring force necessary to overcome such high pressures in the pipeline is further aggravated by the back pressure in the sample collection system. The sample collection system has a back pressure normally associated with the sample collection system. The sample collected by the sample collection apparatus must ordinarily be removed from the sample collection device through a tubing into a sample collection bottle. The difference in sample collection bottles pose a problem for the sample collection apparatus. Consider the following three exemplarly sample collection bottles. Assume simply that the sample collection line is placed in a bucket to collect a sample, in which event, the back pressure is atmospheric pressure. That, at least, provides a relatively constant and low back pressure in the sample collection system. There are other sample collection bottles which are closed chambers. The first portion of collected sample is collected at atmospheric back pressure. However, the sample collection bottle does not have a vent, and the pressure within the bottle increases. The pressure may well increase to an extremely high pressure, and this high back pressure is a force added to the spring acting on the check valve. This inevitably creates a different set or trip point at which the check valve opens. A third type of sample collection bottle is one which provides a relatively constant back pressure. This can be treated as the atmospheric back pressure sample collection bottle described above. While it may be not be atmospheric, the pressure is at least fixed or relatively constant.
A relatively constant back pressure thus equates to an additional constant force acting on the check valve.
Pipeline pressure is not perfectly regulated. As pipeline pressure increases, it may reach the point at which the diaphragm motor of the apparatus cannot overcome pipeline pressure. Consider the situation wherein the movable portion of the probe in the sample collection apparatus has a circular area of one square inch and works into a pipeline having a nominal pressure of 500 psi. In this example, 500 pounds of force are required to overcome pipeline pressure. This ignores the force which is required to operate the sample collection probe. Consider the situation in which the pipeline pressure increases to 1,000 psi whereupon 1,000 pounds of force are required to overcome the resistive pressure to operate of the probe. Ordinarily, the device is powered by a diaphragm motor. This device is normally operated at relatively low pressures. If the surface area is twenty-five square inches, only about twenty psi is required at the diaphragm motor to overcome the resistive force preventing insertion of the probe into the pipeline. This leaves substantial force available to compress the resilient plug and operate the sample collection apparatus. However, assume that pipeline pressure is 1,000 psi in which event 1,000 pounds of force, or a pressure of 40 psi in the diaphragm motor is required to simply overcome pipeline pressure. This leaves very little force available to compress the resilient plug to operate the sample collection apparatus.
The present apparatus overcomes this difficulty. In fact, many advantages flow from the incorporation of a pressure balanced check valve. The check valve element is a fairly large telescoping member on the interior of the probe. The lower end is exposed to pipeline pressure. Pipeline pressure is routed through a conduit to the top end of the check valve element and applied there also. The relative cross-sectional area of the two surfaces exposed to the pipeline pressure are made approximately equal so that the check valve element is pressure balanced. Thus, increases or decreases in pipeline pressure simply null by forming relatively equal and opposite forces acting on the check valve element. Then, a small spring can be used to force the check valve element to the closed position, and this spring need never be changed or recalibrated to compensate for operating pressures on the sample collection apparatus. In fact, if the device is installed in the vertical position and sufficient weight is placed on the check valve element, the weight will serve as a return force. By contrast, the device can be operated horizontally or even in an inverted position by simply installing a spring calibrated to overcome the weight of the equipment to force it to the closed condition. The spring, which is thus described, need not overcome pressure differential created forces acting on the check valve element. This has the advantage of operating even with great fluctuations in pipeline pressure. It also is immune to variations in back pressure. Back pressure increases in the probe do not act on the cross-sectional areas of the probe and, therefore, do not upset this relative balance on the check valve element.
These features and others set forth hereinbelow therefore provide a device capable of operation in a wide variety of operating conditions.